Digital audio signals, and digital video signals containing audio signals, are typically transmitted in data streams according to various standards and protocols. A common problem with such audio signals, which may also be referred to as audio streams, is a wide variation in the loudness levels of different portions of the audio encoded within the audio signal. When the audio signal is reproduced as audio, the resulting audible signal has correspondingly large loudness variations. In some situations, portions of an audio signal are intentionally encoded such that they are reproduced at different audio levels. In other cases, different portions of the audio signal are produced independently of one another with the result that they may be encoded to produce audio at different loudness levels.
Many standards and systems for transmitting audio signals (some embedded with a corresponding video signal) allow a plurality of audio signals to be transmitted within a single transport stream. Each audio signal is divided into blocks of data, which are then transmitted as a series of packets. The packets of the different audio signals are transmitted together in the transport stream. In some standards, the different audio signals may be combined by time multiplexing them such that the audio signal is divided into different time slices and each audio signal is assigned one of the time slices. In other standards, the packets corresponding to each signal may be mixed in any order in the transport stream. The packets of each audio signal are tagged with a signal identifier, allowing them to be combined together to assemble the original audio signal.
In a typical audio or audio-visual data transmission system, some transport streams may include a plurality of audio signals, each with a varying audio level. It is desirable to analyze and adjust the audio levels of such audio signals in one or more audio signals such that at least some of the audio signals may be reproduced with a desirable audio level.